The overall quality of platelets for transfusion is not considered satisfactory by most researchers in the field. The problem is due, in part, to the difficulty of collecting and storing these highly reactive cells, and also to the lack of adequate in vitro methods for assessing quality. We have sought to bring methods of modern cell biology to the investigation of the cellular and biochemical basis of the platelet storage lesion. One approach depends upon the observation that the normal discoid ("plate-like") shape of the platelet changes to a spherical shape during storage. This shape transition is thought to correlate with deterioration of function, so that quantitation of discoid morphology could serve as a measure of satisfactory function. We have developed a device that quantitates the discoid morphology of a population of platelets by measuring the optical properties of the population. This measurement is done while the platelets are within a standard container. In order to validate this assay procedure, we must compare the optical measurements on platelets that have been subjected to storage under a variety of conditions with an acceptable assay of platelet function. The clinical bleeding time is accepted by most workers in the field, but it is logistically difficult. The rabbit system obviates the problems encountered with human systems and has been well standardized. We will utilize this technique to obtain bleeding times on rabbits made thrombocytopenic with cytotoxic drugs and anti-platelet antibody, to compare hemostatic function with optical measurements. Platelets will be subjected to storage at different temperatures, inadequate agitation and volume variation. The optical and bleeding time results will be compared.